Heretofore, it has been known to prepare particulate polymer particles by suspension polymerization a subset of which is limited coalescence. During the course of the process, coalescence of the oil (discontinuous phase) droplets in the aqueous (continuous) phase takes place to form larger size oil droplets. These droplets are limited in size by the presence of a suspension stabilizing agent present in the aqueous phase. This stabilizing agent prevents coalescence from taking place by what is generally believed to be a physical phenomenon that being the prevention (by separation) of one particle from wetting another and thereby joining together. U.S. Pat. Nos. 2,886,559; 2,932,629; and 4,163,090 are directed to techniques employing this limited coalescence form of suspension polymerization.
Suspension polymerization techniques are the subject of numerous patents dealing with the preparation of electrostatographic toner particles because these techniques generally result in the formation of toner particles having a substantially uniform size and uniform size distribution. U.S. Pat. Nos. 4,314,932; 4,360,611 and 4,415,644 are representative of suspension polymerization methods employed in toner manufacture.
A problem that occurs when employing suspension polymerization techniques in the preparation of electrostatographic toner particles is that inherently in the operation of this technique, a suspension stabilizer must be employed in the water phase to maintain the oil in water suspension of the monomer particles during the time they are polymerizing in the aqueous phase. Also, the suspension stabilizer is present to cover the surface of the droplets as polymerization proceeds in order to prevent coalescence. In the limited coalescence subset of suspension polymerization, the suspension stabilizing agent is present in an amount such that when the surface area of the suspension stabilizer matches the surface of the oil droplets, coalescence ceases and the particles will not continue to grow in size. Upon separation of thus formed polymer particles from the aqueous phase, the suspension stabilizing agent remains in place and must be removed in order to employ the polymer particles as electrostatographic toner. This is necessary because the presence of the stabilizing agent interferes with the tribo-electric relationship between the carrier particles and the toner particles employed as developers in electrostatographic devices.
Particulate suspension stabilizing agents, such as, silica or aluminum, are extremely difficult to remove from the surface of the polymer particle formed in the suspension polymerization process. Generally, these particles are removed by dissolving in a medium designed for this purpose. When the particulate stabilizing agent is silica, for example, the silica particles are removed from the surface of the polymer particles by dissolution in a strongly basic water solution, potassium hydroxide being generally preferred in this regard. During this operation, however, the polymer particles, particulaly the smaller size paticles, (those less than 6.mu.m) tend to agglomerate and form clumps of particles which defeats the purpose of utilizing the limited coalescence polymerization procedure in the first place to achieve narrow size distribution. In order to prevent the agglomeration of the particles during the removal step of the suspension stabilization agent, it has been found necessary to incorporate in the alkaline solution a surface active agent. Unfortunately, the presence of surface active agents during this step of the process once again interferes with the charging characteristic of the resulting toner particles and in many instances renders the particles formed useless because they do not change properly in contact with the carrier particles required in the electrostatographic process.